Riverine effects on mitochondrial structure of Bornean orangutans (Pongo pygmaeus) at two spatial scales.

We examined mitochondrial DNA control region sequences of 73 Kinabatangan orangutans to test the hypothesis that the phylogeographical structure of the Bornean orangutan is influenced by riverine barriers. The Lower Kinabatangan Wildlife Sanctuary contains one of the most northern populations of orangutans (Pongo pygmaeus) on Borneo and is bisected by the Kinabatangan River, the longest river in Sabah. Orang-utan samples on either side of the river were strongly differentiated with a high Phi(ST) value of 0.404 (P < 0.001). Results also suggest an east-west gradient of genetic diversity and evidence for population expansion along the river, possibly reflecting a postglacial colonization of the Kinabatangan floodplain. We compared our data with previously published sequences of Bornean orangutans in the context of river catchment structure on the island and evaluated the general relevance of rivers as barriers to gene flow in this long-lived, solitary arboreal ape.